This project involves the study of the anatomical properties and organization of cells in the visual system of primates, with emphasis on the retina and the visual cortex. The studies include (1) the electroretinogram (ERG) mediated by blue-sensitive cone signals before and after the staining of putative blue-sensitive cones by tissue-reactive dyes, (2) the distribution patterns of cones in the human donor retinas with a diagnosis of diabetic retinopathy, and (3) the anatomical association of outer-retinal cells selectively stained with tissue-reactive dyes. (1) Evaluation of the spectral properties of the macaque monkey cones selectively stained with tissue-reactive dyes, which have been tentatively identified as the 'blue' cones, has been hindered by the fact that the dye itself alters the spectral transmission of the ocular media. The study of ERG sensitivity of the same animals before and after the selective labeling of the putative blue cones with the clear monochlorotriazinyl reagent Sandospace S, which can be marked with a secondary dye, has continued. This reagent produced a sharp reduction of the test and field sensitivity of the ERG b-wave mediated by blue cone signals, providing further evidence that the above tentative identification is correct. (2) Evidence of a cone population with a point pattern resembling that of cones selectively stained by tissue-reactive dyes was obtained in initial studies of the retinas of diabetic human donors. Although such dyes were not injected into the eyes of these donors, in vitro staining with more conventional dyes showed a differential receptor labeling, in which cones with the pattern mentioned above were found to be more densely stained than other cones. (3) A systematic light-microscope study of the anatomical association of blue cones and horizontal and bipolar cells that have been selectively stained by several tissue-reactive dyes has been initiated in the macaque retina. These studies provide information on the probable retinal circuitry of the blue-sensitive cone pathway of primate retina.